GSI

Tune Measurement and Feedback for Heavy Ion Synchrotrons and Storage Rings at FAIR

ESR:  Rahul Singh (r.singh@gsi.de)
Supervisor:  Peter Forck (p.forck@gsi.de)

The high beam currents that shall be reached in the FAIR synchrotrons can only be achieved with accurate beam parameter control. The determination and correction of the closed orbit and tune is essential for high current operation of the FAIR accelerators to prevent severe beam losses. Due to the fast acceleration of the beam in the high energy synchrotrons SIS18 and SIS100 the closed orbit correction must have a response time in the order of 1 to 10 ms. This is one order of magnitude faster than comparable installations.

Standard methods for tune measurement are based on beam excitation. This normally leads, however, to an emittance increase and is thus non-ideal. Recently, a much gentler excitation has been developed using a digital Phase-Locked Loop PLL method. It has already been successfully applied at RHIC (Brookhaven Laboratory, USA), Tevatron (Fermilab, USA) and the SPS (CERN, Switzerland). Compared to these accelerators, the FAIR synchrotrons will have a much larger tune spread and varying revolution frequencies. Moreover, the reaction time has to be shorter due to the smaller circumference of the FAIR synchrotrons and storage rings.

The digital signal processing foreseen for beam position measurement is a well-suited starting point for the use of advanced closed-orbit feedback. For sensitive tune measurement and feedback a full digital signal path seems favourable and has to be compared to the signal evaluation by analogue means. Within this project, a general feasibility study is being realized with a prototype installation at the existing SIS18 ring.

Diagnostic Methods for Low Ion Current at the FAIR Storage Rings and Transfer-lines

ESR:  Febin Kurian
Supervisor:  Marcus Schwickert (m.schwicker@gsi.de)

The FAIR storage rings have to be capable of operating with very low ion currents, well below 1 μA. In particular in the case of radioactive ion beams and antiprotons the number of stored particles will be too low for standard beam diagnostics devices. For some of the high-energy beam transfer lines diagnostic devices for the nondestructive measurement of ion currents down to the nA regime will be required.

For this purpose, the installation of Cryogenic Current Comparators (CCC) is foreseen, opening a route for non-intercepting and absolute beam current measurement. The basic working principle of this monitor is the determination of the beam’s magnetic field using a sensitive SQUID based magnetic flux detector. In the frame of this project, the design of the monitor is being optimized and a prototype will be built up and commissioned. As a first step the general requirements for a new standardized CCC-prototype with regard to the different installation locations of the FAIR facility are worked out. The design of the high permeability magnetic field sensor is optimized, taking into account of the material science research results achieved by the collaborating partner University of Jena. The SQUID sensor operates at liquid Helium temperature, thus the design of a compact cryostat with a small insertion length is required. Additionally, the whole mechanical detector set up has to be optimized to effectively suppress mechanical vibrations that otherwise would distort the sensitive measurement of the beam’s magnetic field. The project will be finalized with beam tests of the CCC-prototype with slowly extracted beam from the existing SIS 18 synchrotron at GSI.